In the present experiment, the possibility of a direct role of the electrogenic sodium pump in slow synaptic inhibition was tested. The experiments were carried out on the ninth or tenth paravertebral sympathetic ganglia of the bullfrog using the sucrose gap technique. We found that although electrogenic sodium pumping was inhibited by ouabain or potassium-free Ringer, the slow IPSP was not blocked by ouabain and was enhanced in potassium-free Ringer. These data are not consistent with the hypothesis that the slow IPSP results from an activation of the electrogenic sodium pump.